Process of drying gelatine layers



March 11, 1952 Q, DlpPEL Er AL 2,588,811

PROCESS OF DRYING GELATINE LAYERS Filed May 2, 1947 Patented Mar. 11,1952 PROCESS OFDRYIN G GELATINE LAYERS Cornelis `Johannes Dippel, J an4Anthony Lely, vand Johannes Aloysius Maria Dikhoi, Eindhoven,

Netherlands, assignors to .Hartford National Bank and Trust Company,Hartford, Conn., :as

ktrustee .Application Mayz2, 1947, Serial-No. 745,396 `.In theNetherlands .J une -1, 1946 :4 Claims.

In drying gelatine layers, for example in manufacturing photographicmaterial, great diiiculty is encountered in nthat gelatine can onlylbedried very slowly. Theinstallations for makingphotolgraphic materialin which a photo-sensitive gelatine emulsion is provided on a substratumthus become of very large size and hence very expensive. The avoidanceof the formation of dust in vsuch large spaces of several tens of metersin length, which is absolutely necessary for making good photographicmaterial, increases lthe cost to a considerable extent. Furthermore, theusual heating by means of heated dry air has a poor emciency. Similarldiiculties `arise in manufacturing gelatine layers which Ido notcomprise photosensitive compounds such, forexample, as gelatine layerswhich are intended for recording sound by mechanical means, for exampleby cutting a sound track lm or record.

vThe present invention relates to a process of drying gelatine layerswhich permits drying to beteffectedfat aconsiderably .greater speed withthense o'f equipment of verysmall size.

According to .the invention, gelatine layers are dried by heating in anelectric field of high frequency.

Whereas indrying a coagulated gelatine emulsion .by means of heated dryair, as has been usual hitherto, drying may take place only very slowlysince otherwise the gelatine melts and inhomogeneous layers .areobtained. It has been found that theuseof high-frequency drying .permitsthe temperature of the .gelatine layer -to exceed its melting vpointWithout any harmful consequences for the homogeneityof the .gelatinelayer .being involved.

This vaiords vthe k1possibility of .greater speed in the .dryingprocess. According to the invention yan aqueous gelatine `layer which,after drying,

has a thicknessof 100 microns at the most issubjected to an electricfield while passing a stream oigas over the gelatine for dissipating thewater vapour produced, said field being of ysuch irequency .and strengththat the Water is removed within veminutes. .A treatment of five minutesat the most means that .any point .of the layer is subject `tothe .eldfornve minutes at the most.

.Fora better understanding of the .invention it is V,pointed out thatthe reason why melting of the glatine layer need not necessarily resultin any unevenness is probably due to the fact that the Water which is atrst evaporated .is rapidly removedso that partly dried gelatine of lowwater .content .follows almost immediately. This gelatine upon meltingyields amass .of such viscosity that flows or the like which might leadto troublesome unevennesses no longer occur in it. Since the gelatinetreated according to the invention is dried,.at least initially, in themolten state it .is not necessary for the gelatine emulsion, after beingpoured out on a substratum to form a layer, to coagulate before drying,contrary to the drying methods which have been usual hitherto. It isfurther pointed out that a gelatine emulsion of the kind utilized forpouring Aout a layer of uniform thickness usually contains irom180% toA% by weight of water. If such an emulsion is caused tc coagulate bycooling and subsequently heated up, it melts below a temperature of '30C. to forma thin iiuid mass. The water content decreases as the meltingpoint increases. An emulsion which has been dried te a water content ofabout '50% produces .a vmolten mass which exhibits -at 50 C. a viscositysuch that no troublesome flaws occur in it. Gelatine layers ofphotographic films are dried to a water content of `about 15%. With sucha water content the layers are about ten times thinner than in thefreshly-coagulated undried state.

It is evident that the speed of drying is dependent on the thickness ofthe gelatine layer. Layers of a thickness of about 50microns, such asare used .for cutting mechanical sound records, for example sound iilmrecords exhibiting so-called variations in width, Vrequire a drying timelonger than that for layers of from l5 to 20 microns such as are usedfor the ordinary photographic silver halide gelatine material. Accordingto the invention, the last-mentioned layers are adapted to be driedwithin half a minute.

Heating of the gelatine layer is preferably effected by means of anelectric field generated between filamentary or rod-shaped electrodeswhich are arranged parallel to the surface of the layer vand along whichthe gelatin layer is guided in such manner that the lines of -force ofthe eld extend through the material substantiallyin the direction ofmovement. With such an arrangement of the electrodes the lines of forceextend over a comparatively long distance through the layer itself andover only small distance through the medium, for example air, betweenthe electrodes and the material to be dried. This results in an increaseof the efflciency of the eld so that a great amount ci heat may begenerated in the gelatine layer by means of small equipment and ahigh-frequency generator of low power. Although with the .saidarrangement of the electrodes the strength of the iield in the directionof movement of the material is not constant, the result of the treatmentin this direction is homogeneous provided that the movement takes placeat constant speed. The homogeneity in the transverse direction, normalto the direction of movement, may be controlled by the use of electrodesthe length of which is greater than the width of the material. Y

The arrangement of the electrodes is preferably such that, on passingthe electrodes, the gelatine layer is subjected to a field of graduallydecreasing strength, since as the drying process is proceeding and thegelatine contains less water, the watel` is driven out of the gelatinemore slowly, probably due to the fact'that a thin layer of poortransmitting capacity forms on the surface of the gelatine layer.Consequently, the risk of undue heating of the gelatine increases.Although the gelatine in this drying stage exhibits a viscosity suchthat flows in the gelatine need practically not be feared, there is inthis case a risk of the formation of vapour and hence of bubbles in thegelatine layer. A gradually decreasing eld may be obtained by a gradualincrease of the distances between the electrodes between which the fieldis generated, by a, decrease of voltage, and

so on.

As an alternative, weaker heating in the last stage of the dryingprocess may be obtained by treating the gelatine layer in this stagewith cold air.

Local overheating as a result of locally greater intensity of the fieldisr avoided by control of the rate at which the gelatine layer is guidedthrough the iield so that the layer is subject to these points ofhigher-field intensity for a short time only. The rate which ispreferably used is about 0.5 metre per minute. y

The gelatine layer may be guided between the electrodes in thehorizontal position, or in the inclined, for example vertical, position.Any guide rollers or guide paths which may be provided in the electricfield are required to consist of material of low dielectric losses sothat they are not unduly heated. There need be no fear of combustion ofthe substratum, e. g. nitrocellulose for the gelatine due toelectrostatic charges generated by friction on the rollers, since withthe use of the invention the atmosphere in the drying space is notrequired to be as dry as in the usual processes, in which heating anddrying take place by means of heated dry air. i

The amount of gas, for example air, which is guided along the gelatine`layerfor the dissipationof the water vapour is preferably such as to bejust sufficient for the absorption of the eX- pelled water vapourwithout becoming oversaturated. This aiiords the advantage that theamount of air that is directed over the gelatine may be as small aspossible so that the risk of y contamination of the gelatine layer bydust particles is reduced. The amount of air is preferably 100% morethan that which is required for the dissipation of the water vapour.

In the usual process of drying gelatine the amount of air owing along isconsiderable in order to enhance as much as possible the vaporisation ofwater brought about -by the slightly heated and very dry air. With suchlarge Vamounts of air flowing along the gelatine the risk ofcontamination by dust particles is very great. `According to theinvention, the'air is preferably guided along the material in the samedirec- 4 tion as that in which the material is moved. The air thus firstcomes into contact with the moistest gelatine from which a great amountof water is required to be absorbed quickly and at which the temperatureis'required to be lowest. During flowing through the heating device thetemperature of the air increases. This is not objectionable since themelting point of the gelatine with which it is in contact also rises asthe Water is driven out and the viscosity of the melted and partly driedgelatine is such that unevenness due to iiaws in the gelatine do notarise. On the contrary, this heating of the air is advantageous sincethe capacity of air to absorb water vapour increases as the temperaturerises. The air thus remains capable of absorbing water vapour from thegelatine, which is advantageous since the water vapour may thus beabsorbed by a small amount of air.

. It is further pointed out that in drying gelatine layers in anelectric field the heat is largely generated in the gelatine and thesubstratum is hardly heated due to the fact that the dielectric lossesof a dry substratum-are considerably lower than those of a wet gelatinelayer. Y

The invention is advantageously applicable not only to drying gelatinelayers that are freshly applied but also to drying gelatine layerswhich, after drying, are moistened again, for example photographicmaterial which is developed, fixed and rinsed. f Y

The invention will be described in connection with the following exampleand the accompanying drawing in which:

Fig. 1 shows one form of apparatus for drying film; and

Fig. 2 shows another form of apparatus for drying film.

Escample A band of nitrocellulose having a width of 16 mms. and athickness of microns has applied to it a gelatine layer by treatmentwith a solution containing 20% of gelatineat about 35 C. and bycoagulation of the emulsion. Subsequently, the layer is guided in thevertical direction from below to above, at a speed of 0.7 meter perminute, through van electric field having a frequency of 15megacycles/sec. and a power of 80 watts, the layer being dry within 15seconds. About 35 liters of air per minute at the ambient temperature isdirected along the layer. The thickness of the layer in the dried stateis about 25 microns. The electrode System used for generating theelectric field is shown diagrammatically in the accompanying drawing.Reference numeral l indicates the nitrocellulose band'which is providedwith a gelatine layer and which is moved from below to above. which arevarranged. to be mutually shifted are rod-shaped and have a diameter of3.5 mms. and a length of 20 mms. All the electrodes on the same side ofthe band are interconnected in a conductive manner and are energized byan r-f oscillator 3. The lowermost seven electrodes are at a distance of2 mms. from the band and exhibit a mutual spacing of 10 mms. Theremaining electrodes are at a distance of 4 mms. from the band andexhibit mutual distances of 30 mms. The electrode system is arranged ina tube 4 consisting of material of low dielectric losses through which astream of air is passed by means of an exhaust fan 5 in Fig. l or bymeans of a blower system comprising an intake fari 0 and an exhaust Theelectrodes 2 What we claim is:

1. A process of drying gelatine layers, having a thickness when dried ofless than approximately 100 microns comprising the steps of subjectingthe gelatine layer containing Water to an alternating electric eld ofhigh frequency having an intensity at which the gelatine is heated to atemperature at which it melts and the Water removed therefrom within veminutes, and passing a gas stream over the gelatine layer to remove thewater vapor expelled from the Wet gelatine layer.

2. A process of drying gelatine layers, having a thickness when dried ofless than approximately 20 microns comprising the steps of subjectingthe gelatine layer containing water to an alternating electric eld ofhigh frequency having an intensity at which the gelatine is heated to atemperature at which it melts and the Water removed therefrom Withinone-half a minute, and passinga gas stream over the gela tine layer toremove the Water vapor expelled from the Wet gelatine layer.

3. A process of drying gelatine layers, having a ,A

thickness when dried of less than approximately 100 microns comprisingthe steps of passing the gelatine layer containing water through analterf hating electric eld of high frequency having an intensity atwhich the gelatine is heated to a temperature at which it melts and thewater removed therefrom Within ve minutes at a speed exceeding one-halfmeter per minute, and passing a gas stream over the gelatine layer toremove the Water vapor expelled from the Wet gelatine layer.

4. A process or drying gelatine layers, having a thickness when dried ofless than approximately 100 microns comprising the steps of passing thegelatine layer containing Water through an alternating electric eld ofhigh frequency having lines of force extending substantially parallel tothe direction of motion of the layer and having an intensity at whichthe gelatine is heated to a temperature at which it melts and the waterremoved therefrom within five minutes at a speed of at least one-halfmeter per minute, and passing a gas stream over the gelatine layer toremove the water vapor expelled from the wet gelatine layer.

CORNELIS JOHANNES DIPPEL.

JAN ANTHONY LELY.

J OHANNES ALOYSIUS MARIA DIKHOFF.

REFERENCES CITED The following references are of record in the ille ofthis patent:

UNITED STATES PATENTS Number Name Date 2,042,145 Darrah May 26, 19352,226,871 Nicholas Dec. 31, 1940 2,231,457 Stephen Feb. 11, 19412,291,807 Hart, Jr. Aug. 4, 1942 2,402,609 Brabander June 25, 19462,459,623 Cohoe et al Jan. 18, 1949 2,473,251 Hsu June 14, 1949 FOREIGNPATENTS Number Country Date 691,038 Germany May l5, 1940

1. A PROCESS OF DRYING GELATINE LAYERS, HAVING A THICKNESS WHEN DRIED OFLESS THAN APPROXIMATELY 100 MICRONS COMPRISING THE STEPS OF SUBJECTINGTHE GELATINE LAYER COMTAINING WATER TO AN ALTERNATING ELECTRIC FIELD OFHIGH FREQUENCY HAVING AN INTENSITY AT WHICH THE GELATINE IS HEATED TO ATEMPERATURE AT WHICH IT MELTS AND THE WATER REMOVED THEREFROM WITHINFIVE MINUTES, AND PASSING A GAS STREAM OVER THE GELATINE LAYER TO REMOVETHE WATER VAPOR EXPELLED FROM THE WET GELATINE LAYER.